The present invention for clarity will be described in relation to its use on xerographic drums or belts; however, the use of this blade in or on other photoconductive surfaces such as endless belts, plates or other photosensitive surfaces of a xerographic system are intended to be included, if suitable.
In marking systems such as Xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the photoreceptor surface. The charged toner being electrostatically attached to the latent electrostatic image areas creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to a final support material, such as paper, and the toner image is usually fixed by fusing thereto to form a permanent record corresponding to the original.
In some Xerographic marking systems, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the xerographic process. Since the photoreceptor surface is reusable, the toner image is then transferred to a final support material, such as paper, and the surface of the photoreceptor is prepared to be cleaned and used once again for the reproduction of a copy of an original. In this endless path, several Xerographic related stations are traversed by the photoconductive drum or belt.
Generally, in one embodiment, after the transfer station, a photoconductor cleaning station is next and it generally comprises a cleaning brush and a blade or a cleaning blade alone which is used to remove residual debris from the drum or belt such as toner, toner additives and other filming materials. This film is generally caused by the residual toner being impacted onto the drum or belt by the cleaning brushes and/or blades. When the lubrication of this blade is below a necessary level, it will abrade the belt. Toner is the primary lubricant for the blade; however, a problem is with good cleaning efficiency by the cleaning brushes, the amount of toner reaching the blade can often be well below this necessary level. Without proper lubrication, or if the blade is composed of the wrong material, this blade can seriously abrade the belt.
Since most toners used today are negatively charged, the embodiments throughout this disclosure and claims will be described relating to the use of a negative toner; however, when a positive toner is used, the proper opposite adjustments can easily be made.
The brush above mentioned in prior art systems is responsible for nearly all of the filming on the photoconductive (PC) belt or drum. This brush is positively charged to attract a negative charged toner and remove most of it from the PC belt or drum. Adjacent to the first brush is a vacuum which vacuums the toner from the brush for later disposal. The vacuum is adjacent to the brush and should vacuum off of the brush some residual positively charged toner. Then, as above noted, the cleaning blade scrapes off the belt any remaining toner debris or film layer. If suitable, the cleaning blade can be used in a xerographic system without the brush or brushes. As above noted, the cleaning blade will remove the film layer comprised of toner and toner additives that may be caused by the impact of the cleaning brush against the toner and PC drum or belt.
Many of the low volume electrophotographic printers and some high speed marking apparatus comprising amorphous silicon photoreceptors (a-Si) use elastic polyurethane blades to remove residual toner from drum or belt. Improvements in the reliability of such blades are desired to minimize/reduce wear induced defects and to extend the overall life of the cleaning blade and the drum or belt. Polyurethane and other elastomeric materials are typically used in prior art cleaning blade materials. Improved blade materials are required on a-Si photoconductive surfaces to extend the useful life of both the blades and the a-Si photoconductive surface.
The use of prior art polyurethane cleaning blades with amorphous silicon photoreceptive surfaces are described in U.S. Pat. Nos. 6,226,479; 6,453,137; and 6,233,417.
Amorphous silicon (a-Si) photoreceptors have very hard, long wearing surfaces. The hardness of the surface enables long photoreceptor life, but due to the low wear rate films and oxidation can build-up on the photoreceptor surface. The conventional urethane blade cleaner for a-Si photoreceptors do not sufficiently abrade the surface of the photoreceptor to eliminate the films and oxidation. This leads to the need for a buffing of the photoreceptor surface by a service technician to remove the films and oxidation. More recently abrasive particles have been added to the toner to increase wear of the photoreceptor by the cleaning blade. Abrasive toner additives sometimes have eliminated the need for photoreceptor buffing. Since abrasive toner additives increase blade wear as well as photoreceptor wear, the life of the cleaning blade is substantially reduced. Amorphous silicon photoreceptors are advertised to have lives up to 5 Mp, but the polyurethane cleaning blades with them typically last to 20% or less of the photoreceptor life.